Recording materials to which the principle of color development resulting from a reaction between a leuco chromogen and a color developer is applied have been widely used for thermal sensitive recording papers for output recordings by facsimiles, printers or the like or pressure sensitive copy papers for slip books simultaneously transcribing multiple sheets, because such recording materials can be recorded by using a simpler recording apparatus in a short time without undergoing any troublesome procedures such as development, fixing, etc.
It is desired for the recording materials described above, the one which can develop color faster, retain clear whiteness of the uncolored area (hereinafter represented as "background"), and provide high toughness in the developed images and the background. Recently, a great amount of recording materials have been consumed particularly in a field such as labeling where the reliability of recorded images is critically demanded. Accordingly, the recording materials capable of providing colored images being stable in long term to plasticizers and fat and oils those are contained in the organic macromolecules used as packaging materials has been intensively desired. Many efforts have been made to provide such recording material from various points of view, such as leuco chromogen, color developing agent, addition of stabilizer, etc. Nevertheless, the material with desired properties mentioned above has not been developed.
Diphenyl sulfone derivatives are known as useful as a recording material similar to the compound of the present invention. They are well known as a color developer used for recording materials. Diphenyl sulfone derivatives one of which phenyl is substituted with alkoxy or aralkyloxy and the other phenyl is substituted with hydroxyl are proposed as a color developer in Japanese Patent Laid-opened No. Sho 57-210886, No. Sho 58-20493, No. Sho 58-82788, No. Sho 58-132593, and No. Sho 60-13852, and World Open WO 84/02882. However, any of them are not sufficient in the stabilizing property for the developed images.
For improving the long term stability of the colored images described above, many patent applications covering the recording materials comprising a epoxy group such as novolac epoxy resin or glycydyl compound have been filed. The applicant of the present invention has also filed a patent application (World open WO 93/06074) wherein 4-hydroxy-4'-(2-methylglycydyloxy)diphenyl sulfone is disclosed as a recording material. However, all of the recording materials disclosed in the patent applications described above are not sufficient yet for the practical use in terms of staining of the background and the long term stability of the colored images.
As described above, in recent years, improvement in long term stability of the colored images developed on the recording material, particularly improvement in resistance to plasticizers have particularly been expected. It is an object of the present invention to provide a recording material superior in giving long term stability of colored image which can thereby solve the problems described above.